The present invention generally relates to an exhaust gas cleaner for a diesel engine and, more particularly, to a control system for the cyclic rejuvenation of the exhaust gas cleaner.
In a diesel engine power plant, it is well known to use an exhaust gas cleaner for minimizing the emission of obnoxious particulates, particularly carbon particulates, carried in the exhaust gases emerging from the diesel engine. Earlier works were to construct the exhaust gas cleaner mainly with a filter having a multiplicity of tortuous flow passages defined therein for trapping and collecting carbon particulates carried by the exhaust gases. With this type of cleaner, it has been found that, although the carbon particulates collected by the filter can be effectively incinerated during the high load engine operating condition at which the temperature of the exhaust gases emitted is sufficiently high enough to allow them to be combusted, they tend accumulate in the filter to such an extent as to result in the clogging of the flow passages in the filter during the other engine operating condition than the high load operating condition, that is, during the medium or low load engine operating condition at which the exhaust gas temperature is relatively low. When the clogging of the flow passages with the carbon particulates takes place in the filter, the back-pressure increases, resulting in the undesirable operating characteristic of the engine. This has to be avoided in view of the fact that the engine is more frequently operated under the medium or low load condition than under the high load condition.
Accordingly, a sophisticated exhaust gas cleaner available today comprises, in addition to the filter, a burner adapted to be regularly and at periodic intervals operated to heat the exhaust gases to a temperature high enough to allow the carbon particulates trapped in the filter to be combusted. Examples of cleaners of the type described above are disclosed, for example, in Japanese Laid-open Patent Publication No. 49-71315, published July 10, 1974; U.S. Pat. Nos. 4,167,852 and 4,335,574, patented Sept. 18, 1979 and June 22, 1982, respectively; Japanese Patent Publication No. 57-38765, published Aug. 17, 1982; and U.S. Pat. Nos. 4,345,431 and 4,372,111, patented Aug. 24, 1982 and Feb. 8, 1983, respectively.
In any of these prior art cleaner systems, a combustion aiding air is supplied under predetermined pressure to the burner regardless of the pressure dominant inside a burner chamber and, accordingly, the flow of the combustion aiding air is susceptible to change with change in pressure inside the burner chamber which would occur in accordance with the operating conditions of the diesel engine. Once this happens, the air-fuel mixing ratio of a combustible mixture to be combusted within the burner chamber deviates, resulting not only in the insufficient production of heat energies with the carbon particulates consequently incinerated ineffectively, but in the incomplete combustion with a large amount of carbon components consequently discharged to the atmosphere.